Electronic and electrically powered locks are known in many varieties. All kinds of them use some electrical servomechanism to block the locking-unlocking function such as moving a latch or a bolt or to perform the locking-unlocking itself. Most often, the servomechanism is a solenoid which is a simple, rugged, low cost, reliable and durable mechanism. In a solenoid mechanism, the armature performs a simple linear or swinging motion under the action of electromagnetic forces and elastic elements. It may be held in one or more positions by a permanent magnet, as in the known bi-stable solenoid.
The simplicity of the motion is however accompanied by a major problem, which is that the armature may be moved also by an inertial force. Such force may be created by a shock applied on the lock as a whole, especially on a pendant padlock, but also on safes, cassettes, etc. Also, vibrator may be used to create periodical acceleration in parts of a lock. In this way, a solenoid mechanism may be switched into unblocked or open state without any key or coded input. Many complicated ways have been developed to overcome this problem. They require complex additional parts, space in the padlock and are not reliable in all positions of the padlock.
For example, WO 2004/072418 to the same inventor discloses an anti-shock arrangement comprising a first element mounted to the armature and a second element fixed to the solenoid stator. The first element is engaged to the second element so as to perform a helical motion when the armature performs the linear motion. The helical motion is associated with overcoming a predetermined friction force, thereby preventing the two motions under shock applied on the whole device along the armature axis but allowing the linear motion under the magnetic action of the solenoid coil.
U.S. Pat. No. 5,249,831 describes a lock having a counterweight connected through a lever to a spring-actuated lock bolt on a safe to balance out any inertial forces tending to move the bolt out of its locking position when the safe is struck a heavy blow.
U.S. Pat. No. 4,412,436 describes a time lock for bank vault doors with a shock-resistant plunger latching mechanism having a relatively massive counterweight to oppose dynamic forces during shocks. The counterweight is balanced by a spring so as to unload the clock mechanism which blocks and unblocks a door bolt. A gear train is introduced between the locking device and a relatively small mass to increase the virtual inertia of the system, and an elastic link is provided between the input of the lock and the mass enabling the system to absorb vibrations at the input.